This patch defines PCIe ring buffer array pointer as void instead
of mwifiex_pcie_buf_desc. This will enable us to use same pointers
for ring operations instead of new structures if buffer descriptor
structure changes.

Also split out event buffer descriptor structure from struct
mwifiex_pcie_buf_desc. For PCIe8766 TX/RX buffer descriptor is
same as evevt buffer descriptor. Newer chips could use different
TX/RX buffer descriptor while event descriptor remains the same.
Signed-off-by: NAvinash Patil <patila@marvell.com>
Signed-off-by: NBing Zhao <bzhao@marvell.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>